Shrouded electro-magnetic apparatus



Sept. 3, 1957 w. A. G. BUSSING 2,805,275

SHROUDED ELECTROMAGNETIC APPARATUS Filed July 11, 1951 '1' r 'r 4 w 1 M,- w A a VI v 'iilml jnmul mum INVENTOR WILHELMUS ANTONIE G ERARDUS BUSSIM United States Patent 2,805,275 SHROUDED ELECTRO-MAGNETIC APPARATUS Wilhelmus Antonie Gerardus Bussing, Eindhoven, Netherlands, assignor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application July 11, 1951, Serial No. 236,228 Claims priority, application Netherlands July 13, 1950 2 Claims. (Cl. 174-52) This invention relates to electro-magnetic more particularly to transformers or chokes, which are shrouded at least in part and a metal mass of good heatconductivity, introduced in a solid condition, being arranged between the apparatus and the shroud.

In a known form of such shrouded apparatus, the metal mass referred to is constituted by oxidised aluminium balls, which are arranged between the energising coil and the box-shaped yoke of an electro-magnet and which are preferably linked by putty. This mass acts to cool the col Manufacture of aluminium balls, which can hardly be used for other purposes, is not cheap. The subdivision of the mass in balls requires a binder to assist in the arrangement and to avoid rattling. However, the binder adversely affects the thermal conductivity of the mass.

The said disadvantages are avoided and in addition supplementary advantages are obtained if according to the invention, the mass is constituted by creased foil of nonmagnetic material, for example of aluminium.

In this case the use of this mass enables the form of the apparatus to be altered to accord with the shape of the shroud and a further mass of substantially even thickness may be arranged between the apparatus thus completed and the shroud. This provides excellent cooling with the use of means adapted to be manufactured at low cost.

The filling factor of the mass is preferably from 0.05 to 0.3, which is defined as the ratio of the weight of the filling mass to the Weight of a solid mass of the same material having the same volume. The foil mass is provided with a creased surface by crumpling up, then pinched together into the desired form, for example into a plug and eventually pressed between the apparatus, or a component member of the apparatus, and the shroud. The pressing pressure optimum for cooling has been found experimentally to be defined by the said value of the filling factor.

The foil to be used is preferably from to 100 microns thick. The price of thinner foils is comparatively high and thicker foils are difiicult to machine.

In a particularly efficient embodiment of the invention a substantially hum-free construction of the electro-magnetic apparatus is achieved, while conserving efficient cooling, if the said mass constitutes the only mechanical link between the apparatus and the shroud.

In order that the invention may be readily carried into effect, two examples will now be described in detail with reference to the accompanying drawings, in which:

Fig. 1 is a plan view of a choke,

Fig. 2 is a side elevation of this choke when housed in metal housing, and

Fig. 3 is a side elevation of a different choke, which is secured to a mounting rail.

Referring to the figures, 1 designates the ferro-magnetic part, built up from iron sheets, of the choke coils illustrated, which are intended for use, for example, as

apparatus series impedances of a gas discharge lamp. The winding of the chokes is designated 2.

The shell-type choke shown in Fig. 1 is arranged in a rectangular, closed aluminium box 3 (Fig. 2). The contour of the choke as shown in Fig. 2 is not similar to the form of the box. The form of the choke is altered to conform with the box with the use of four plugs of squeezed aluminium foil 4. The space between the choke thus completed and the box is filled with a layer 5 of creased aluminium foil of substantially even thickness.

The creased foil masses 4 and 5 constitute the only mechanical joint between the iron circuit and/or the winding of the choke and the box shrouding this choke. It has been found that owing to the resilient bedding of the choke in the creased foil material the mechanical vibrations set up in the choke during normal operation are substantially prevented being transmitted to the box, so that the latter can be secured without inconvenience to another body, for example to the fixture of a fiuorescent lamp the choke of which constitutes the series impedance, without the other body risking to act as a sound board, converting the mechanical vibrations of the choke into interfering noise, sometimes referred to as hum.

The current leads of the winding of the choke are not shown in the figures. As usual they are resiliently passed through the box 3 at two points insulated from each other so that they do not constitute any mechanical link between the box and the choke that is liable to transmit oscillations.

The core-type choke shown in Fig. 3 is secured, by means of L-shaped stay members 6, for example by means of screw connections not shown, to a mounting rail 7 surrounding the choke only in part. Arranged between the coil 2 of the choke and the bottom of the rail 7 is a plug of crumpled up aluminium foil 8.

For information it must be mentioned that the electromagnetic apparatus shown in Figs. 1 and 2 has a power of 160 VA. and a copper and iron loss of 28 W. The plugs 4 and the layer 5 are constituted by aluminium foil 50 microns in thickness and grams in weight, the filling factor being 0.24. Measurements undertaken with this apparatus provided with a foil mass and with the same shrouded apparatus provided with aluminium balls of 2 millimetres diameter, 285 gins. total weight and a filling factor of 0.56, no binder being used, showed, after the stationary final condition was reached, the following temperature image:

The use of the invention consequently enabled obtainment of cooling means which are more effective, materially lighter and much more readily and cheaply made and which in addition are free from rattling. If this cooling agent constitutes the only mechanical link between the apparatus and the shroud a substantially hum-free construction is achieved.

What I claim is:

l. A high-heat-conductivity supporting structure for an electro-magnetic device having an uneven surface contour comprising a substantially rigid supporting member enclosing said device and spaced therefrom, a plurality of wadded masses of irregularly crumpled thin metal foil each constituted by a heat conductive non-magnetic material positioned in depressions of the uneven surface contour of said device to produce therewith an even contour, and a plurality of creased thin sheets of said metal foil interposed between the even contour of said device and said masses and said member, the metal foil constituting the only mechanical link between the device and the supporting member, whereby a substantially hum-free construction is obtained. 2. A high'heat-conductivity supporting structure to an electro-magnetic device as claimed in claim 1 in which the filling factors of the masses is between 0.05 and 0.3, and in which the metal foil is aluminum having a thickness'between about 10 and 100 microns.

References Cited in the file of this patent UNITED STATES PATENTS Westberg July 9, Kiesel Oct. 10, Linder Aug. 25, Wood Mar. 9, Venable July 18,

FOREIGN PATENTS Great Britain July 6, 

